Shock sensors are used in motor vehicles, including cars and aircraft, to detect vehicle collisions. When such a collision occurs, the shock sensor triggers an electronic circuit for the actuation of one or more safety devices. One type of safety device, the deployable air bag, has found widespread acceptance by consumers as improving the general safety of automobile operation. Air bags have gone from an expensive option to standard equipment in many automobiles. Further, the number of air bags has increased from a single driver's side air bag to passenger air bags. Future use of multiple air bags is a distinct possibility.
With the ever increasing utilization of air bags, research and development has continued with efforts to make air bags and the electronics and sensors which control their deployment both more reliable and of lower cost. A key aspect of reliability with respect to air bags involves the twin, somewhat conflicting requirements that the air bag deploy in every situation where deployment would be advantageous to the passengers but, at the same time, not deploy except when actually needed. Reliable deployment of an air bag without unwanted deployments is facilitated by use of multiple sensors in combination with actuation logic which can assess the nature and direction of the crash as it is occurring and, based on preprogrammed logic, make the decision whether or not to deploy the air bag. This increase in reliability tends to lead to a greater number of sensors as well as increased use of electronic logic.
The desire to hold down sensor cost and to keep the sensor integrated with the logic circuits has led to the use of solid state shock sensors. However, solid state shock sensors are prone to losing touch with the real world and may occasionally indicate a crash is occurring due to radio frequency interference, electronic noise, cross-talk within the electronics, etc.
The ability of mechanical shock sensors as an integral part of bag deployment systems to prevent unnecessary bag deployment has kept demand for mechanical shock sensors high.
A number of types of shock sensors employing reed switches have been particularly advantageous in combining a mechanical shock sensor with an extremely reliable electronic switch which, through design, can be made to have the necessary dwell times required for reliable operation of vehicle safety equipment. The reed switch designs have also been of a compact nature such that the switches may be readily mounted on particular portions of the vehicle which, in a crash, will experience a representative shock which is indicative of the magnitude and even the direction of the shock-inducing crash.
Typically, shock sensors have sensed crash magnitude and direction. Information about the type of crash a vehicle is experiencing is then used by safety equipment logic to deploy air bags or retract seat belts, etc. One result of a vehicle crash or accident can be an over turning, or roll-over of the vehicle. Such events may be preceded by a side impact or may be the result of a loss of control of the vehicle. In either case a side crash load may or may not be detected prior to the vehicle entering a roll. If safety equipment logic is to consider the implications of vehicle roll-over in deploying safety equipment, then sensors must be provided which can reliably indicate a roll-over has occurred or is occurring. Typically integrated accelerometers and rate sensors are employed to characterize vehicle dynamics. However, such solid state devices are subject to electromagnetic interference.
What is needed is a mechanical roll-over sensor